This invention relates to coatings for surgical implants. In particular, the present invention relates to hydrophilic, covalently cross-linked copolymers that are covalently bound to the surface of surgical implants.
Both rigid and foldable implantable ophthalmic lens materials are known. The most common rigid material used in ophthalmic implants is polymethyl methacrylate (xe2x80x9cPMMAxe2x80x9d). Foldable intraocular lens (xe2x80x9cIOLxe2x80x9d) materials can generally be divided into three categories: silicone materials, hydrogel materials, and non-hydrogel (xe2x80x9chydrophobicxe2x80x9d) acrylic materials. See, for example, Foldable Intraocular Lenses, Ed. Martin et al., Slack Incorporated, Thorofare, N.J. (1993). For purposes of the present application, hydrophobic acrylic materials are acrylic materials that absorb less than approximately 5% water at room temperature.
Silicone and non-hydrogel acrylic materials used in ophthalmic implants can potentially damage endothelial cells and perhaps other cells or tissues as well during or after the implant""s insertion in the eye. These materials are generally hydrophobic and/or tacky and can pull cells off of eye tissues that contact the implant. Particularly in the case of phakic IOL""s implanted between the capsular bag and the iris, there is significant potential for physical contact between the implant and surrounding cells or tissue even after the implant reaches its target location.
The present invention relates to hydrophilic coating compositions for surgical implants, particularly ophthalmic implants comprising silicone, hydrophobic acrylic or hydrogel materials. More specifically, the present invention relates to a copolymeric coating material for an implant where the copolymeric coating material is capable of absorbing from about 40 to about 70% water and comprises
(i) 2-phenylethyl (meth)acrylate;
(ii) a hydrophilic monomer selected from the group consisting of hydroxyalkyl (meth)acrylates; and acrylamides; and
(iii) a reactive plasticizer selected from the group consisting of polyethylene glycol (200-2000) mono(meth)acrylates and polyethylene glycol (200-2000) monomethylether mono(meth)acrylates.
The present invention also relates to methods for applying the copolymeric coating material as specified above to an implant""s surface. In one embodiment, the method comprises dissolving the copolymer containing a latent cross-linking agent in a solvent to form a coating solution, contacting the coating solution with the implant""s surface, and activating the latent cross-linking agent in the coating copolymer. In another embodiment, the method comprises dissolving the copolymer in a solvent to form a coating solution, adding a cross-linking agent to the coating solution, contacting the coating solution with the implant""s surface, and heating the coated implant to generate cross-linking.
Unless indicated otherwise, all amounts are expressed as weight %.
The coating material of the present invention is a copolymer comprising:
(i) 2-phenylethyl (meth)acrylate;
(ii) a hydrophilic monomer selected from the group consisting of hydroxyalkyl (meth)acrylates; and acrylamides; and
(iii) a reactive plasticizer selected from the group consisting of polyethylene glycol (200-2000) mono(meth)acrylates and polyethylene glycol (200-2000) monomethylether mono(meth)acrylates.
The coating material contains 2-phenyethyl (meth)acrylate in an amount generally ranging from 20-60%. The most preferred 2-phenylethyl (meth)acrylate is 2-phenylethyl methacrylate (xe2x80x9c2-PEMAxe2x80x9d).
The coating material contains an amount of hydrophilic monomer generally ranging from 20-40%. Preferred hydrophilic monomers are hydroxyalkyl (meth)acrylates. Most preferred are 2-hydroxyethyl methacrylate; 1,3-dihydroxypropyl methacrylate; 2,3-dihydroxypropyl methacrylate; mixtures of 1,3- and 2,3-dihydroxypropyl methacrylate (xe2x80x9cGMMAxe2x80x9d); monomethoxy glyceryl methacrylate; and mixtures thereof.
Suitable reactive plasticizers or softening agents include polyethylene glycol (200-2000) mono(meth)acrylates and polyethylene glycol (200-2000) monomethylether mono(meth)acrylates. These ingredients can reduce or minimize haze or crazing. Methacrylates are preferred, with PEG(400)monomethylether monomethacrylate most preferred. The amount of the reactive plasticizer will range generally from about 20 to about 40%. Depending on the implant""s function and the thickness of the coating, some degree of haze or crazing may be tolerated such that large amounts of the reactive plasticizer may not be required.
The coating material is capable of absorbing from about 40 to about 70% water, preferably from about 42 to about 55% water. The proportion of the copolymer""s monomers will depend on the desired water content. In a preferred embodiment, the desired water content is about 42 to about 55% and the coating material is comprises from 25 to 40% of 2-PEMA, from 20 to 40% of GMMA, and from 20 to 40% of polyethylene glycol (400) monomethylether monomethacrylate.
In one embodiment, in addition to the ingredients described above, the coating material also comprises a latent cross-linking agent, such as a blocked isocyanate. Suitable blocked isocyanate compounds include imidazole blocked isocyanatoethyl methacrylate. In this embodiment, the latent cross-linking agent is copolymerized with the other ingredients of the coating copolymer. In an alternative embodiment, the cross-linking agent is not added until the point where the coating copolymer is dissolved to form a coating solution. Examples of cross-linking agents that are suitable for use in this alternative embodiment include di-imidazole blocked 1,12-isocyanatododecane and peroxides, such as benzoyl peroxide and 2,4-dichlorobenzoyl peroxide.
The amount of the cross-linking agent contained in the coating compositions of the present invention will depend upon, among other factors, the chosen cross-linking agent and the degree of cross-linking desired. In general, the amount of the cross-linking agent necessary to cross-link the coating composition and secure it to the implant""s surface will be about 0.5-3% for blocked isocyanates and about 3-6% for peroxides.
The copolymeric coating material is prepared by combining the chosen 2-phenylethyl (meth)acrylate, hydrophilic monomer, reactive plasticizer, and a polymerization initiator (optionally with a latent cross-linking agent) to form a coating composition and then curing the coating composition. Any type of polymerization initiator may be used, including thermal initiators and photoinitiators, provided that the initiator can be activated without activating the latent cross-linking agent if present. Preferred initiators are UV- and blue-light activated initiators. The most preferred initiator is the benzoylphosphine oxide initiator, 2,4,6-trimethyl-benzoyidiphenylophosphine oxide (xe2x80x9cTPOxe2x80x9d), which is activated by blue-light. The amount of the polymerization initiator in the coating compositions of the present invention will depend upon the curing conditions. In general, however, the amount will be about 3% (w/w) or less, preferably about 2% (w/w) or less, and most preferably about 1% (w/w).
In order to prevent premature cross-linking, the coating compositions of the present invention do not contain significant amounts of monomers having more than one unsaturated bond. Such ingredients include the common cross-linking monomers ethyleneglycol dimethacrylate; diethylene glycol dimethacrylate; ethyleneglycol diacrylate; allyl methacrylates; allyl acrylates; 1,3-propanediol dimethacrylate; 1,6-hexanediol dimethacrylate; 1,4-butanediol dimethacrylate; polyethyleneoxide diacrylates; and the like.
In addition to the 2-phenylethyl (meth)acrylate, hydrophilic monomer, plasticizer, any latent cross-linking agent, and polymerization initiator, the coating compositions optionally include one or more ingredients selected from the group consisting of UV absorbers that are copolymerizable with the 2-phenylethyl (meth)acrylate, hydrophilic monomer and reactive plasticizer; blue-light blocking colorants that are copolymerizable with the 2-phenylethyl (meth)acrylate, hydrophilic monomer and reactive plasticizer; and chain transfer agents to retard cross-linking within the coating copolymer.
Ultraviolet absorbing chromophores can be any compound which absorbs light having a wavelength shorter than about 400 nm, but does not absorb any substantial amount of visible light. Suitable copolymerizable ultraviolet absorbing compounds are the substituted 2-hydroxybenzophenones disclosed in U.S. Pat. No. 4,304,895 and the 2-hydroxy-5-acryloxyphenyl-2H-benzotriazoles disclosed in U.S. Pat. No. 4,528,311. The most preferred ultraviolet absorbing compound is 2-(3xe2x80x2-methallyl-2xe2x80x2-hydroxy-5xe2x80x2-methyl phenyl) benzotriazole. Suitable polymerizable blue-light blocking chromophores include those disclosed in U.S. Pat. No. 5,470,932. If a blue-light activated polymerization initiator is chosen and a blue-light blocking colorant is added, the polymerization initiator identity or concentration may have to be adjusted to minimize any interference.
The chain transfer agent, if present, is typically added in an amount ranging from 0.01 to 0.4%. Many chain transfer agents are known in the art. Examples of suitable chain transfer agents include 1-dodecanethiol and 2-mercaptoethanol.
After the coating copolymer is polymerized, a coating solution is prepared by dissolving the coating copolymer in a solvent or mixture of solvents, such as a 50:50 (parts by weight) mixture of ethanol and 2-pentanone. The solvent or mixture of solvents is preferably chosen to give a clear, homogenous coating solution where the chosen solvent or solvent mixture does not evaporate so quickly that it leaves a hazy coating. If no latent cross-linking agent was included in the coating copolymer, a cross-linking agent, such as di-imidazole blocked 1,12-isocyanatododecane or a peroxide, is added to the coating solution.
The concentration of the coating copolymer in the coating solution will depend on the desired coating thickness. Other factors that will influence the thickness of the coating include the viscosity of the coating solution, the temperature of the coating solution and the implant, and the evaporation rate of the chosen solvent(s). In general, the coatings of the present invention will be no more than 1 xcexcm thick, and preferably will be about 0.5 xcexcm thick. A minimum coating thickness of about 0.01 xcexcm is likely necessary to allow the coating to survive any manipulation of the implant (such as the folding of an IOL) and any abrasion caused during implantation or extended residence at the target site in a patient. A concentration of coating copolymer of about 7-9% in the coating solution will typically produce a coating about 0.5 xcexcm thick in a dip-coating process.
The coating solution is applied to the implant by conventional techniques, such as spin- or dip-coating processes. Dip-coating is preferred. The implant is preferably dipped quickly so as to minimize any swelling of the implant caused by the solvent in the coating solution.
After the coating is applied to the implant, the coating is dried. A two-stage drying process is preferred. First, the coated implant is allowed to dry in air until most or all of the solvent has evaporated (generally xe2x89xa615 minutes). Second, the coated implant is baked at elevated temperature, about 80-110xc2x0 C., to eliminate as much of the remaining solvent as possible and to activate the cross-linking agent. A preferred drying process involves room temperature air drying for 15 minutes, followed by baking at 100xc2x0 C. for about 2 hours for blocked isocyanate cross-linking agents and 110xc2x0 C. for about 3-5 hours for peroxide cross-linking agents.
Once the coating is secured to the implant""s surface by covalent bonds formed by activating the cross-linking agent, the coating cannot be removed by solvents or solvent mixtures, including the same solvent used as the base in the preparation of the coating solution. After the coating is covalently-bound to the implant""s surface, any impurities or unbound ingredients in the coating (or implant) may be removed by extraction in a suitable solvent, such as acetone in the case where the implant is an ACRYSOF(copyright) IOL. It is important that the swell response of the coating and the substrate to the extraction solvent not be too different in order to prevent damage to one or both during the extraction process. To prevent crazing or cracking of the coating, the swell of the coating should be greater than or equal to that of the substrate.
Before the coated implant is manipulated, the coating is preferably hydrated for several seconds to minimize crazing or other damage to the coating.
The implants suitable for coating with the hydrophilic coatings of the present invention are preferably made of hydrophobic acrylic materials, but could also be constructed of silicone, silicone-acrylic copolymers or hydrogels. The coating material should be selected so that it is not identical to the implant or xe2x80x9csubstratexe2x80x9d material that is to be coated. Additionally, the coating material should be selected so that it is capable of absorbing a greater amount of water (i.e, a higher water content material) than the substrate material. Preferred implant or substrate materials include the acrylic materials described in U.S. Pat. Nos. 5,290,892 and 5,693,095, the entire contents of which are hereby incorporated by reference. In the case where the implant is an IOL, the coatings of the present invention may be used in conjunction with substrate materials intended for use as a xe2x80x9chardxe2x80x9d IOL (that is inserted in an unfolded state) or a xe2x80x9cfoldablexe2x80x9d or xe2x80x9csoftxe2x80x9d IOL (that is inserted in a folded or compressed state). For example, the IOL material to be coated could be those IOL materials disclosed in U.S. Pat. Nos. 5,693,095 or 5,331,073. The coating may be applied to the entire IOL or to only a portion of the IOL. As used herein, xe2x80x9cimplantsxe2x80x9d includes contact lenses.
In order to prepare the implant material to be coated so that it is capable of receiving the coating, it may be necessary or desirable to expose the surface to be coated to a reactive plasma gas prior to applying the coating composition of the present invention. Suitable reactive plasma gases include oxidizing gases, such as oxygen gas. A suitable plasma chamber is the P2CIM B-Series plasma chamber made by Advanced Plasma Systems, Inc. Using such a chamber, suitable plasma parameters include: power=400 W, plasma gas oxygen; pressure of the plasma gas=225 mTorr; exposure time=4-6 minutes.
The following examples are intended to be illustrative but not limiting.